Yo! Right, the Burton sizing is about 8 - 11 for a medium binding, so you might just be able to squeeze those hoofs into them (it might take some cramming though) and if not, then your going to be wanting larges. You may also want to look for a boot that has some kind of reduced foot print technology in it so that the Bindings might last you a little longer.

My suggestion would be to take your bindings in with you when you do decide to fork out/pick up your boots and check them then to see if the boot is gonna fit. Thats the only way your gonna know.